Enhancing uric acid electrochemical detection with copper ion-activated mini protein mimicking uricase within ZIF-8: response surface methodology (RSM) optimization.

This study aims to investigate the influence of copper(II) ions as a cofactor on the electrochemical performance of a biocomposite consisting of a mini protein mimicking uricase (mp20) and zeolitic immidazolate framework-8 (ZIF-8) for the detection of uric acid. A central composite design (CCD) was utilized to optimize the independent investigation, including pH, deposition potential, and deposition time, while the current response resulting from the electrocatalytic oxidation of uric acid was used as the response. The statistical analysis of variance (ANOVA) showed a good correlation between the experimental and predicted data, with a residual standard error percentage (RSE%) of less than 2% for predicting optimal conditions. The synergistic effect of the nanoporous ZIF-8 host, Cu(II)-activated mp20, and reduced graphene oxide (rGO) layer resulted in a highly sensitive biosensor with a limit of detection (LOD) of 0.21 µM and a reproducibility of the response (RSD = 0.63%). The Cu(II)-activated mp20@ZIF-8/rGO/SPCE was highly selective in the presence of common interferents, and the fabricated layer exhibited remarkable stability with signal changes below 4.15% after 60 days. The biosensor's reliable performance was confirmed through real sample analyses of human serum and urine, with comparable recovery values to conventional HPLC.

Rational design of mini protein mimicking uricase: Encapsulation in ZIF-8 for uric acid detection.

Five mini proteins mimicking uricase comprising 20, 40, 60, 80, and 100 amino acids were designed based on the conserved active site residues within the same dimer, using the crystal structure of tetrameric uricase from Arthrobacter globiformis (PDB ID: 2yzb) as a template. Based on molecular docking analysis, the smallest mini protein, mp20, shared similar residues to that of native uricase that formed hydrogen bonds with uric acid and was chosen for further studies. Although purified recombinant mp20 did not exhibit uricase activity, it showed specific binding towards uric acid and evinced excellent thermotolerance and structural stability at temperatures ranging from 10°C to 100°C, emulating its natural origin. To explore the potential of mp20 as a bioreceptor in uric acid sensing, mp20 was encapsulated within zeolitic imidazolate framework-8 (mp20@ZIF-8) followed by the modification on rGO-screen printed electrode (rGO/SPCE) to maintain the structural stability. An irreversible anodic peak and increased semicircular arcs of the Nyquist plot with an increase of the analyte concentrations were observed by utilizing cyclic voltammetry and electrochemical impedance spectroscopy (EIS), suggesting the detection of uric acid occurred, which is based on substrate-mp20 interaction.

Fabrication of calix[4]arene/polyurethane for the adsorptive removal of cationic dye from aqueous solutions.

Calix[4]arene/polyurethane (C4PU) has been synthesized and characterized as an alternative adsorbent for the adsorption of methylene blue (MB) and malachite green (MG) dyes from the aqueous solution. C4PU was synthesized by reacting p-tert-butyl calix[4]arene with hexamethylene diisocyanate (HMDI) as the cross-linking agent. Different polymer ratios were synthesized, and C4PU-4 shows better adsorption than other ratios. The polymer was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) analysis, and point of zero charges (pHPZC). The isotherms and kinetics of the adsorption of MB and MG were studied under a range of experimental conditions, including pH, adsorbent dosage, initial dye concentration, and contact time. The adsorption was determined by the adsorption percentage of MB and MG dyes from the solution. The Langmuir isotherm model best describes the adsorption process for both dyes, and it follows a pseudo-second-order kinetic model, with the maximum adsorption capacity (qmax) of MB and MG, respectively, was found to be 1.991 mg·g-1 and 2.240 mg·g-1.

Portable electrochemical immunosensor for detection of Mycobacterium tuberculosis secreted protein CFP10-ESAT6 in clinical sputum samples.

An early detection of Mycobacterium tuberculosis is very important to reduce the number of fatal cases and allow for fast recovery. However, the interpretation of the result from smear microscopy requires skilled personnel due to the propensity of the method to produce false-negative results. In this work, a portable, rapid, and simple sandwich-type immunosensor reader has been developed that is able to detect the presence of M. tuberculosis in sputum samples. By using sandwich-type immunosensor, an anti-CFP10-ESAT6 antibody was immobilized onto the graphene/polyaniline (GP/PANI)-modified gold screen-printed electrode. After incubation with the target CFP10-ESAT6 antigen, the iron/gold magnetic nanoparticles (Fe3O4/Au MNPs) conjugated with anti-CFP10-ESAT6 antibody were used to complete the sandwich format. Differential pulse voltammetry (DPV) technique was used to detect the CFP10-ESAT6 antigen at the potential range of 0.0-1.0 V. The detection time is less than 2 h. Under optimal condition, CFP10-ESAT6 antigen was detected in a linear range from 10 to 500 ng mL-1 with a limit of detection at 1.5 ng mL-1. The method developed from this process was then integrated into a portable reader. The performance of the sensor was investigated and compared with the standard methods (culture and smear microscopy). It provides a good correlation (100% sensitivity and 91.7% specificity) with both methods of detection for M. tuberculosis in sputum samples henceforth, demonstrating the potential of the device as a more practical screening tool.Graphical abstract.

Bioinspired mp20 mimicking uricase in ZIF-8: Metal ion dependent for controllable activity.

Mini protein mimicking uricase (mp20) has shown significant potential as a replacement for natural enzymes in the development of uric acid biosensors. However, the design of mp20 has resulted to an inactive form of peptide, causing of loss their catalytic activity. Herein, this paper delineates the impact of various metal cofactors on the catalytic activity of mp20. The metal ion-binding site prediction and docking (MIB) web server was employed to identify the metal ion binding sites and their affinities towards mp20 residues. Among the tested metal ions, Cu2+ displayed the highest docking score, indicating its preference for interaction with Thr16 and Asp17 residues of mp20. To assess the catalytic activity of mp20 in the presence of metal ions, uric acid assays was monitored using a colorimetric method. The presence of Cu2+ in the assays promotes the activation of mp20, resulting in a color change based on quinoid production. Furthermore, the encapsulation of the mp20 within zeolitic imidazolate framework-8 (ZIF-8) notably improved the stability of the biomolecule. In comparison to the naked mp20, the encapsulated ZIFs biocomposite (mp20@ZIF-8) demonstrates superior stability, selectivity and sensitivity. ZIF's porous shells provides excellent protection, broad detection (3-100 µM) with a low limit (4.4 µM), and optimal function across pH (3.4-11.4) and temperature (20-100°C) ranges. Cost-effective and stable mp20@ZIF-8 surpasses native uricase, marking a significant biosensor technology breakthrough. This integration of metal cofactor optimization and robust encapsulation sets new standards for biosensing applications.

Enhanced electrochemical detection of iodide at a reduced graphene oxide-modified carbon electrode in iodized salts.

In this study, enhancement of electrochemical performance of electrochemically reduced graphene oxide (ERGO) on a screen-printed carbon electrode (SPCE) (ERGO/SPCE) coupled with ion-pairing (cetyltrimethylammonium bromide, CTAB) for the determination of iodide in table salt has been described. The electrode modification of ERGO/SPCE was conducted using cyclic voltammetric (CV) scanning in the potential range of 1.3-0.4 V for 50 cycles after the drop-casting of graphene oxide (GO) suspension on the SPCE. It was found that the electro-active surface area of ERGO/SPCE was increased by 1.5-fold compared to the bare SPCE. ERGO/SPCE sensor displays linearity towards iodide in the concentration range from 0.020 to 1.0 mg/L (sensitivity = 5.40 µA(mg/L)-1, R2 = 0.9906) with the limit of detection (LOD) and limit of quantitation (LOQ) of 0.070 mg/L and 0.21 mg/L, respectively. The comparison between polarography and ERGO/SPCE sensor was in good agreement.

Polycyclic Aromatic Hydrocarbons: Occurrence, Electroanalysis, Challenges, and Future Outlooks.

The past several decades have seen increasing concern regarding the wide distribution of polycyclic aromatic hydrocarbons (PAHs) in environmental matrices. Primary toxicological data show PAHs' persistent characteristics and possible toxicity effects. Because of this pressing global issue, electroanalytical methods have been introduced. These methods are effective for PAH determination in environmental waters, even outclassing sophisticated analytical techniques such as chromatography, conventional spectrophotometry, fluorescence, and capillary electrophoresis. Herein, the literature published on PAHs is reviewed and discussed with special regard to PAH occurrence. Moreover, the recent developments in electrochemical sensors for PAH determination and the challenges and future outlooks in this field, are also presented.

Designed Mini Protein 20 Mimicking Uricase Encapsulated in ZIF-8 as Nanozyme Biosensor for Uric Acid Detection.

This work presents the use of encapsulated mini protein 20 mimicking uricase (mp20)-zeolitic imidazolate framework-8 (ZIF-8) as a bioreceptor for the development of a nanozyme-based electrochemical biosensor for uric acid detection. The electrochemical performance of the biofunctionalized mp20@ZIF-8 on the reduced graphene oxide/screen-printed carbon electrode (rGO/SPCE) was investigated by optimizing operating parameters such as pH, deposition potential, and deposition time using a central composite design-response surface methodology (CCD-RSM). The quadratic regression model was developed to correlate the combination of each variable to the oxidation current density as a response. A significant effect on current response was observed under optimized conditions of pH of 7.4 at −0.35 V deposition potential and 56.56 s deposition time, with p < 0.05 for each interacted factor. The obtained coefficient of determination (R2) value of 0.9992 indicated good agreement with the experimental finding. The developed nanozyme biosensor (mp20@ZIF-8/rGO/SPCE) exhibited high selectivity in the presence of the same fold concentration of interfering species with a detection limit of 0.27 µM, over a concentration range of 1 to 34 µM. The practicality of the tailored biosensor in monitoring uric acid in human serum and urine samples was validated with high-performance liquid chromatography (HPLC) and a commercial uric acid meter. Hence, nanozyme-based is a promising platform that offers a rapid, sensitive, selective, and low-cost biosensor for the non-enzymatic detection of uric acid in biological samples.

Adsorption of Methylene Blue Dye by Calix[6]Arene-Modified Lead Sulphide (Pbs): Optimisation Using Response Surface Methodology.

Lead sulphide (PbS) modified with calix[6]arene was synthesised as an alternative and regenerative adsorbent for the adsorption of methylene blue (MB) dye. The prepared calix[6]arene-modified PbS was characterised via Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The response surface methodology (RSM) based on the central composite design (CCD) was employed to identify the most significant factors, such as the initial concentration, adsorbent dosage, pH, and temperature, and to optimise the effects of the factors on the adsorptive efficiency as its response. The optimised initial concentration, adsorbent dosage, pH, and temperature were 20.00 mg/L initial concentration, 44.00 mg calix[6]arene-modified PbS, pH 6, and a temperature of 31.00 °C. A good correlation between the values and well-fitted model was observed. The adsorption performance was evaluated based on the percentage removal of MB dye from the water system. The adsorption isotherm best fit the Langmuir isotherm model, and the adsorption rate was followed by a pseudo-second-order kinetic model, a single layer chemical adsorption with a maximum adsorption capacity (qmax) of 5.495 mg/g.

Enhancement the electrochemical conductivity of a modified reduced graphene oxide/calixarene screen-printed electrode using response surface methodology.

In this paper, Response Surface Methodology with central composite design (RSM/CCD) was used to optimize a modified electrode for improved electron transfer rate and electrochemical performance. The modification was done on a screen-printed carbon electrode (SPCE) with reduced graphene oxide (ERGO)/calix [4] arene (ERGOC4-SPCE). The properties of the modified electrodes were analyzed via cyclic voltammetry, Raman spectroscopy, and Fourier-Transform Infrared (FT-IR) spectroscopy. Then, different variables were optimized, namely, the concentration of graphene oxide, GO (A), the number of scan cycles of graphene oxide (B), and the deposition time (C). The effect of the optimized variables on the reduction-oxidation peak current response of the potassium ferricyanide redox system was analyzed. By using statistical analysis, it shows a significant effect of the concentration of GO, the deposition time, and the number of scans cycles on the peak current response. The coefficient of determination (R2) value of 0.9987 produced indicated a good fit of the model with experimental finding.

Photoluminescence Investigation of Carrier Localization in Colloidal PbS and PbS/MnS Quantum Dots.

The existence of surface organic capping ligands on quantum dots (QDs) has limited the potential in QDs emission properties and energy band gap structure alteration as well as the carrier localization. This drawback can be addressed via depositing a thin layer of a semiconductor material on the surface of QDs. Herein, we report on the comparative study for photoluminescent (PL) properties of PbS and PbS/MnS QDs. The carrier localization effect due to the alteration of energy band gap structure and carrier recombination mechanism in the QDs were investigated via PL measurements in a temperature range of 10-300 K with the variation of the excitation power from 10 to 200 mW. For PbS QDs, the gradient of integrated PL intensity (IPL) as a function of excitation power density graph was less than unity. When the MnS shell layer was deposited onto the PbS core, the PL emission exhibited a blue shift, showing dominant carrier recombination. It was also found that the full width half-maximum showed a gradual broadening with the increasing temperature, affirming the electron-phonon interaction.

Polymer Pen Lithography-Fabricated DNA Arrays for Highly Sensitive and Selective Detection of Unamplified Ganoderma Boninense DNA.

There is an increasing demand for lithography methods to enable the fabrication of diagnostic devices for the biomedical and agri-food sectors. In this regard, scanning probe lithography methods have emerged as a possible approach for this purpose, as they are not only convenient, robust and accessible, but also enable the deposition of "soft" materials such as complex organic molecules and biomolecules. In this report, the use of polymer pen lithography for the fabrication of DNA oligonucleotide arrays is described, together with the application of the arrays for the sensitive and selective detection of Ganoderma boninense, a fungal pathogen of the oil palm. When used in a sandwich assay format with DNA-conjugated gold nanoparticles, this system is able to generate a visually observable result in the presence of the target DNA. This assay is able to detect as little as 30 ng of Ganoderma-derived DNA without any pre-amplification and without the need for specialist laboratory equipment or training.

Enhancing a clenbuterol immunosensor based on poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube performance using response surface methodology.

Clenbuterol (CLB) is an illegal antibiotic for livestock, which is misused as a growth promoter drug. In this study, an immunosensor modified with poly(3,4-ethylenedioxythiophene) (PEDOT), multi-walled carbon nanotubes (MWCNT) and anti-clenbuterol antibody (Ab) was developed for the detection of CLB. A screen-printed carbon electrode (SPCE) was modified with PEDOT/MWCNT as a sensor platform before immobilizing Ab for specific CLB binding through a competitive-type immunoassay. Free CLB in the sample solution competed with clenbuterol-horseradish peroxide (CLB-HRP) to bind with Ab. A high current signal was obtained after optimization of the electrochemical immunoassay conditions (pH, incubation temperature, antigen (Ag) incubation time and % blocking) using the response surface methodology/central composite design (RSM/CCD). The developed immunosensor is highly reproducible and sensitive with good storage stability, which are necessary for practical application. In real sample application, this immunosensor produces comparable results with liquid chromatography-mass spectrometry; thus, it is useful for CLB screening and monitoring in real meat samples.